Such antenna systems are previously known, e.g. from the published international patent applications WO 96/37922 A1 and WO 02/35651 A1 (both in the name of Allgon AB). In these known systems, the tilt adjusting mechanism comprises a mechanical rod, which is linearly movable back and forth and which extends through an opening in the bottom end wall of the casing for manual or motor driven actuation so as to effect the desired adjustment of the electrical tilt setting.
For manual operation, the rod may be formed with a pinion engaging with a gear mechanism coupled to a control knob which can be manually turned around. In motor driven systems, see e.g PCT/SE2005/001777 (Powerwave Technologies Sweden AB), an electrical motor, such as a stepping motor, is arranged below the antenna casing and is connected with a driving gear to the rod with the pinion for moving the rod which extends through the wall of the antenna casing.
A proposal has also been made to couple a motor-driven member by a magnetic coupling with coupling members located inside and outside the antenna casing. See PCT/SE2005/001776 (Powerwave Technologies Sweden AB).
Moreover, it is also well-known to effect the desired adjustment by remote control of such an electric motor being connected to the tilt adjustment mechanism, see e.g. the patent specification U.S. Pat. No. 6,198,458 B1 (Deltec). Here, the entire control system, including the tilt adjustment mechanism, the electric motor and most of the associated electronic circuitry, is disposed inside the antenna casing.
The above-mentioned systems are relatively complicated and expensive to manufacture. However, antennas sometimes have to be replaced so as to meet new requirements and standards, and such replacement or upgrading is therefore very expensive since all parts of the system, including the antenna elements, the feed structure, the tilt adjusting mechanism and the control system, have to be replaced.
A proposal permitting replacement of the control system for a base station antenna is disclosed in the published international patent application WO 02/061877 (Kathrein).
Here, the entire control system, including the electronic circuits and an electrical motor, is mounted in a separate unit outside the antenna casing, so as to permit replacement. The displaceable mechanical element, in the form of a rotatable shaft, extends through an opening at the bottom of the antenna casing and engages with the electric motor (or a drive member coupled thereto). Of course, such separate units are also relatively expensive to replace at the antenna site. Moreover, mechanical elements disposed partially outside the antenna casing are exposed to the prevailing climatic conditions and have to be sturdy and weather resistant.